Humidity-responsive automatic dryer control system



1966 J. D. HARNDEN, JR 3,269,027

HUMIDITY-RESPONSIVE AUTOMATIC DRYER CONTROL SYSTEM Filed Feb. '7, 1964. 5 Sheets-Sheet 1 1% E w V32.

1 S2. A VP )6 INVENTOR.

Tomd D. HARMDEUMR,

m ATT Y Aug. 30, 1966 J. D. HARNDEN, JR 3,269,027

HUMIDITY-RESPONSIVE AUTOMATIC DRYER CONTROL SYSTEM Filed Feb. '7, 1964 3 Sheets-Sheet 2 I N VENTOR.

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H 1 s ATTORNEY JOHN D. HARNDENJJR.

1966 J. D. HARNDEN, JR 3,269,027

HUMIDITY-RESPONSIVE AUTOMATIC DRYER CONTROL SYSTEM Filed Feb. '7, 1964 5 Sheets-Sheet 3 INVENTOR.

J'OHN D. HARNDENIJE Hi5 ATTORNEY United States Patent 3,269,027 HUMIDITY-REfiPONSHVJE AUTOMATIQ DRYER CONTROL SYSTEM John I). Harnden, In, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York Filed Feb. 7, 1964, Ser. No. 343,313 9 (Ilairns. (Cl. 34-43) This invention relates to automatic dryers, and more particularly to a humidity-responsive automatic control system for such dryers.

The automatic termination of operation of a fabric dryer when the fabrics are dry is well known. In the past, various factors have been used to determine dryness of the clothes. These include, for instance, substantial rises in the exhaust air temperature, conductivity of fabrics across a pair of conductors, and the like. While the use of a humidity sensor might seem like an obvious approach where humidity is the ultimate factor, it has been found exceedingly difficult to use any such device. One major reason is that atmospheric humidity varies substantially, and unless the device is recalibrated for each drying operation inaccurate control is achieved. A solution to this is to provide sensing of the atmospheric conditions, and determine when the humidity of the exhaust air has returned to that of the atmosphere. Here again though, the fact that the air being exhausted from the dryer is at a relatively high temperature compared to atmosphere has made such an approach very difiicult, since the amount of moisture that air can contain varies substantially with its temperature.

An important aspect of my invention lies in the provision of a system which will provide a reliable signal from humidity-sensing means. It is, therefore, an object of my invention to provide an improved automatic dryer control circuit utilizing humidity-sensing means.

More specifically, it is an object of my invention to provide humidity-sensing means responsive to atmospheric conditions, and humidity-sensing means responsive to dryer exhaust conditions, and to cause termination of the drying operation when the proper relationship exists between the two sensing means.

Yet a further more specific object of my invention is to provide an arrangement which provides for cooling of the humidity-sensing means in the dryer exhaust substantially to atmospheric temperature, so that in effect the two sensing means are both at atmospheric temperature, and therefore a simple correlation between the two can be provided.

In carrying out the invention in one form thereof I provide a fabric drying machine which has, in the usual way, a fabric container. Suitable means are provided for circulating air into the container through an appropriate air inlet, and then out of the container through an air outlet which communicates with atmosphere through an outlet conduit means. This outlet conduit means includes a protected portion which is so formed that it receives a small air fiow compared to the air flow through the remainder of the conduit means. Together with this air circulation system, I provide a heater positioned to supply heat to the fabrics in the container so as to cause vapor migration from the clothes, the vapor or moisture then being carried off with the exhaust air.

A first humidity-sensing means is provided in the protected portion of the conduit means so as to be cooled by atmospheric air substantially to atmospheric temperature, and a second humidity-sensing means is positioned to sense atmospheric conditions. When the two humiditysensing means provide approximately the same signal, it means that the air leaving the dryer has the same humidity content as atmospheric air, and that therefore no further moisture is being removed from the fabrics, i.e., the

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fabrics are dry. This intelligence is used, in conjunction with control means, to cause the control means to effect termination of the operation of the heater.

The subject matter which I regard as my invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. My invention, both as to organization and method of operation together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings.

In the drawings:

FIGURE 1 is a side elevational view of a clothes dryer incorporating my improved dryer control arrangement, the view being partly broken away and partly sectionalized to illustrate details;

FIGURE 2 is a top elevational view, partly in cross section and partly broken away, of the dryer in FIG- URE 1;

FIGURE 3 is an enlarged fragmentary view, partly in cross section, showing an important feature of my invention;

FIGURE 4 is a circuit diagram illustrating the improved control system of my invention; and

FIGURE 5 is a view, similar to the view of FIGURE 3, of a modification of my invention.

Referring now to FIGURES 1 and 2, the machine illustrated is a domestic clothes dryer generally indicated by the numeral 1. Dryer 1 is provided in the usual way with a cabinet 2 having a front door 3 to provide access to the interior of the cabinet for loading or unloading clothes. Provided on the top wall 4 of the cabinet is a control panel 5 which may, in the conventional way, in clude a suitable manual control 6 connected to a sequence control assembly 7 mounted in panel 5. By manual presetting of control 6 the machine may be caused to start, and automatically proceed through a cycle of operation. Within cabinet 2, there is provided a clothes tumbling container or drum 8 mounted for rotation on a substantially horizontal axis. Drum 8 is substantially cylindrical in shape, having a first outer cylindrical wall portion 9, second and third outer cylindrical wall portions 10 and 11 located respectively adjacent the front and back of the drum, a front wall 12 and a back wall 13. Outer wall portions 9, 10 and 11 are imperforate over their entire length so that the outer shell of the basket is imperforate. On the interior surface of central portion 9 there may be provided a plurality of clothes tumbling ribs 14 so that the clothes are lifted \up when the drum rotates, and then are tumbled back down to the bottom of the drum. The front of drum 8 may be rotatably supported within outer casing 2 by suitable idler wheels 15. These wheels are rotatably secured to the top of a member 16 which extends up from base 17 of the machine. Wheels 15 are disposed beneath the drum in contact with portion Ilti thereof so as to support portion 10 on each side to provide a stable support.

The rear end of drum 8 receives its support by means of a stub shaft 18 extending from the center of wall 13. Shaft 18 is secured within a bearing 19 formed in a battle 20 which in turn is rigidly secured to the back wall 21 of cabinet 2 by any suitable means such as, for instance, welding at a number of points 22. With the arrangement shown, the basket may rotate on a horizontal axis with rollers 15 providing the front support, and stub shaft 18 within bearing 19 providing the rear support.

In order to provide for the flow of a stream of drying air through the clothes drum, the drum is provided with a central opening 23 in its front wall 12 and with an opening in the form of a plurality of perforations 24 in its rear wall 13, the perforations in the present case being formed to extend around the rear wall in an annulus.

As has been stated, baifle member 29 is rigidly secured to rear wall 21 of cabinet 2. Baffle member also serves to support heating means such as electrical heating elements 25 appropriately insulated from the baffle member. Elements 25 may be annular in shape so as to be generally coextensive with perforations 24 in drum 8. A baffle member 26 is rigidly secured to the back wall 13 of the drum outside the ring of perforations 24 and within the stationary baflie 20, so that an annular air inlet 27 is in effect formed by the baffles 20 and 26. In this manner, an inlet passage is formed for air to enter annular inlet opening 27 between the baflies, pass over the heater 25, and then pass through openings 28 formed in baflie 26 to the interior of drum 8.

The front opening 23 of the drum is substantially closed by means of a stationary bulkhead generally indicated by the numeral 29. Bulkhead 29 is made up of a number of adjacent members including the inner surface 30 of access door 3, a stationary frame 31 for the door formed as a flange of front wall 32 of the cabinet, the inner surface member 33 of an exhaust duct which is formed by the cooperation of member 33 with the front wall 32 of the cabinet, and an annular flange 34 mounted on frame 31 and on the duct Wall. It will be noted that a suitable clearance is provided between the inner edge of the drum opening 23 and the edge of bulkhead 29 so that there is no rubbing between the drum and the bulkhead during rotation of the drum. In order to prevent any substantial air leakage through opening 23 between the interior and the exterior of the drum, a suitable ring seal 35, preferably formed of felt-like material, is secured to flange 34 in sealing relationship with the exterior surface of drum Wall 12.

Front opening 23, in addition to serving as part of the air flow path through the drum, also serves as a means whereby clothes may be loaded into and unloaded from the drum. Door 3, whose inner surface forms part of the bulkhead closing the opening, is mounted on cabinet 2 so that when the door is opened clothes may be inserted into or removed from the drum through the door frame 31. It will be noted that the door includes an outer flat imperforate section 36 and an inwardly extending hollow section 37 mounted on the flat outer section. Hollow section 37 extends into the door frame 31 when the door is closed, and the door surface 30 which comprises part of the combination bulkhead 29 is actually the inner wall of the hollow section.

The air outlet opening from the drum is provided by a perforated opening 38 formed in the inner wall 30 of hollow door section 37. The bottom wall section of door 3 and the adjacent wall of door frame 31 are provided with aligned openings 39 and 40, opening 40 providing the entrance to the duct 41 formed by the cooperation of member 33 with front wall 32. As shown, a lint trap 42, which may comprise a fine mesh bag, is preferably positioned in the exhaust duct 41 at opening 40, the bag being supported by the door frame 31.

Duct 41 leads downwardly to an opening 43 formed in the member 16 which supports wheels 15. Opening 43 constitutes the inlet to a blower member 44 contained within a housing 45 and directly driven by an electric motor 46. The blower draws ambient air in through an inlet opening 47 which, for purposes which will appear more fully herebelow, is positioned quite close to the housing 45 of blower 44. This air then passes to the back of the dryer, and after passing through inlet 27 it passes over the heaters 25 so as to be heated, and then through the basket, entering the basket through openings 24-7 The air leaves the basket through screened opening 38 and passes down through openings 39 and 40 into duct 41.

From duct 41, the air is then passed by blower 44 through i an outlet conduit 48 (FIGURE 2) to an opening 49 formed in the housing 2. The exhaust passage from drum 8 which includes the hollow section 37 of the door,

the duct 41, the interior of blower housing 45, and the conduit 48 form outlet conduit means connecting the drum to atmosphere so that after air has been passed over the clothes it may then be exhausted to atmosphere. It will also be seen that, in effect, the cabinet forms a conduit, guiding the air entering inlet 47 to the annular inlet 27, the heaters 25 and the basket 8.

In addition to driving blower 44, motor 46 constitutes the means for effecting rotation of drum 8. In order to effect this, motor 46 is provided with a shaft 50 having a small pulley 51 formed at the end thereof. A belt 52 extends around pulley 51 and also entirely around the cylindrical wall section 9 of drum 8. The relative circumferences of pulley 51 and wall section 9 cause the drum to be driven by the motor at a speed suitable to effect tumbling of the clothes therein. In order to effect proper tensioning of belt 52 there may be provided a suitable idler assembly 53 secured on the same support 54 which secures one end of the motor. Thus, the air is pulled through the drum; at the same time the fabrics in the drum are tumbled, and when the air is heated by heating elements 25 the heated air passing through the drum causes vaporization of moisture from the clothes. The vapor is carried off with the air as it passes out of the machine.

A humidity sensing assembly 55 is included in the exhaust conduit means. Specifically, in the present case, the assembly is secured on the blower housing 45 in such a position that, as shown in FIGURE 1, there will be a substantial passage of atmospheric air over assembly 55. Assembly 55 is mounted to the blower housing 45 by means of a mounting member 56, preferably formed of insulating material. The blower housing 45 has a pair of openings 57 and 58 formed therein so that, in effect, member 56 and the housing 45 together form a relatively secluded portion or chamber 59. While chamber 59 will have some of the exhaust air passing therethrough, it will have a relatively slow air flow compared to the rest of the exhaust conduit means.

Member 56 supports assembly 55 which, as shown in FIGURE 3, preferably includes a sheet-like member 60 of insulating material. On the inside surface of member 60, that is, within portion 59, there is provided a first humidity-sensitive structure 61. In the conventional way, humidity-sensing device 61 may be formed of a pair of grids 62 and 63, such as are schematically shown in FIGURE 4, wherein the grids provide conductors closely spaced apart over a substantial length. The operation of such a device is conventional, and is effected by having the amount of moisture in the air control the conductivity between the grids; as the moisture content of the air increases, the conductivity between the grids increases. A like device 64 is provided on the outside of sheet 60, that is, there is a second humidity-sensing structure 64 having grids 65 and 66. Sensor 64, as can be seen from FIG- URES 2 and 3, is so positioned that the air entering opening 47 passes directly over it. The arrangement shown is such that, because of the relatively small air flow through chamber 59, and because of the substantial amount of air being passed over the exterior of chamber 59, both humidity sensors 61 and 64 operate at almost the same temperature.

The operation of dryer 1 is controlled by the new and improved control system shown in the circuit diagram of FIGURE 4. As shown therein, the system may be energized across a three wire power supply system which includes supply conductors 67 and 68 and a neutral coniductor 69. For domestic use, conductors 67 and 68 will normally be connected across a 220 volt power supply with 110 volts appearing between the neutral line 69 and each of the conductors, and with the neutral line being at ground voltage. Motor 46, connected between conductors 67 and 69, is a single phase induction type motor having a main winding 70 and a start winding 71 both connected at a common end through a conductor 72 to a conventional door switch 73 (which is closed when door 3 is closed and is opened when the door is open). Conductor 72 is connected to conductor 69.

Start winding 71 is connected in parallel with main winding 76 under the control of a speed responsive device, such as that shown at 74, which is schematically shown as connected to the rotor '75 of the motor. Speed responsive device 74 controls a switch 76 which is engageable with either a contact 77 or a contact '73, being engaged with contact 77 when the motor is at rest and moving into engagement with contact 78 as the motor comes up to speed. It can readily be seen that engagement with contact 77 connects the start winding 71 in parallel with main winding 76, while movement of switch '76 away from this position opens the start winding. Thus, as rotor 75 comes up to speed the start winding becomes de-energized, and the motor then continues to run on the main winding 79 alone.

The starting of the motor is provided by a manually operable switch 79 which may, for instance, in the structure of FIGURE 1, be moved to its closed position by pulling out on member 6. Switch 79 connects the motor to supply conductor 67 through contacts 81) and 81 of a switch 82 which also includes a third contact 83. Switch 79 is normally biased to the open position shown. However, when member 6 is pulled out manually, and provided contacts 81 and 81b of switch 82 are closed, energization of the motor is provided. Within less than a second (under normal circumstances) the motor comes up to speed so that switch 76 engages contact 78. As a result of this movement of the centrifugally operated switch 76, the main winding 79 of motor 46 continues to be energized by a bypass around switch 79 when member 6 is released and switch 79 opens.

A timer motor 8 3 controls a pair of earns 85 and 86. Cam 85 in turn controls switch 82, and cam 86 controls a switch 87. The two cams are also movable by rotation of member 6, so that when operation of the machine is desired member 6 may be rotated until cam 85 closes all three contacts of switch S2 and cam 86 closes the other timer operated switch 87. The machine operation is terminated, as will be seen herebelow, when cam 85 has been rotated sufiiciently by the timer motor 84 to open the contacts of switch 82.

An energizing circuit is completed for heater 25 through the following circuit. Starting at conductor 67 the circuit proceeds through contacts 81 and 83 of switch 82, and then through a conductor 88 including a conventional temperature controlling thermostat 89 to heater 25. The circuit then proceeds through a conventional safety thermostat 90 to a conductor 91 leading back through a switch 92 to conductor 68 to complete the circuit. Switch 92 is controlled by the centrifugal member 74, being closed only when the motor has come up to speed so that there can be no energization of heater 25 except when motor 46 is operating properly.

It can be seen that the timer motor 84 is energized across conductors 67 and 69 through switch 87. In addition, in parallel with switch 87 there is provided a switch 93 controlled by a relay 94 which forms part of the improved control arrangement of my invention.

In summary, when operation of the machine is desired, switch 79 is closed to start the motor, assuming that there has been closure of switch 82. As soon as the motor comes up to speed, switch 79 may be released and the motor will continue to run on winding 70 alone as de scribed. Also, upon closure of switch 82 thetimer motor is running, its energization being completed through either of switches 87 and 93. Switch 87, under the control of cam 86, provides a predetermined period of operation of the timer 34 and then opens so that the timer then ceases to operate provided, as will be explained herebelow, that the switch 93 has been opened. The drying operation will then continue until the clothes are substantially dry, at which time, as will be explained herebelow, switch 93 closes. The closure of switch 93 re-energiz'es the timer motor 84 which then tolls out the cycle to cause opening of the three contacts 80, 81 and 83, thereby terminating operation of the machine. Of course, as usual, the three contacts may either be opened together, or else contact 83 alone may be opened first, leaving an additional period of motor operation to provide a tumbling cool-down of the clothes.

The arrangement for controlling the operation of the machine includes a transformer 95 having a primary winding 96 which, through a core 97, provides power to secondary windings 98 and 99. Winding 99 provides power to a Wheatstone bridge which includes as its four legs humidity sensors 61 and 64, and a variable resistor 1% split into two resistances 101 and 102.. Resistances 1'91 and 192 are so adjusted that when the resistances of the two humidity sensors approach equality so as to indicate dryness, the bridge will be substantially balanced. Between the tWo humidity sensors 61 and 6d, the bridge is connected through an appropriate resistance 103 to the base 104 of a conventional transistor generally indicated at 195. Between resistors 191 and 1112, the bridge is connected through a conventional rectifier 166 to the emitter 197 of the transistor.

When the Wheatstone bridge is balanced, there will be little or no voltage difference between the base 104 and the collector 197. However, in the event of an unbalance occurring in the bridge, the transistor will then be provided with a bias in the forward direction; depending upon the extent of the bias there will be current passed from the emitter 107 to collector 198. Relay 94 is connected in a circuit so that, when sufficient current is passed from the emitter to the collector, then the secondary winding 98 is able to energize the relay and cause it to open switch 93.

When the humidities sensed by sensors 61 and 64 are essentially the same, the bridge is substantially balanced and therefore relay 94 is not energized. This is, in effect, the condition which exists at all times except when moisture is being evaporated from clothes within the machine and there is therefore more moisture in the exhaust from the machine than in the atmosphere. In operation then, when the machine is started the heater will heat the air passing over the clothes in drum 8, and evaporation of the moisture from the wet clothes will start. In a minute or two, this evaporation of moisture will change substantially the amount of moisture in the exhaust air compared to the amount of moisture in the atmosphere. Because of this, sensor 61 will become substantially more conductive than sensor 64, thereby unbalancing the bridge with the result that relay 94 is energized and switch 93 is opened. Since switch 87 is opened after a predetermined period of time, for instance 5 minutes, this means that after 5 minutes of operation the timer motor will cease its advance. This situation will continue to prevail as long as relay 944 is energized, and the relay will continue to be energized as long as there is an unbalance in the bridge caused by greater conductivity of sensor 61 than of sensor 64.

It will be recognized that during this period a substantial quantity of airtaken directly from atmosphereis being passed over member 60 and member 56 so as to cool the inner surface of member 60 substantially down to the temperature of the atmosphere. Therefore, with substantially the same temperatures prevailing for both sensors 61 and 64, the humidity readings they provide relative to each other are a true indication of whether there is still moisture being removed from the clothes in the machine. Consequently, when the conductivity of sensor 61 decreases back approximately to the same as that of sensor 64, the bridge becomes balanced as it was at the beginning of the operation; when the bridge is balanced, there is no longer enough voltage between base 164 and collector 107 for the collector to pass enough current to the emitter to energize relay 94. As a result, relay 94 becomes de-energized and switch 93 closes. The closure of switch 93 re-energizes the timer motor which then tolls out the cycle to terminate operation of the machine. In testing of the structure of my invention, it was found that, with a ten volt input, a decrease to 0.5 volt, sufficiently low for re-energization of the timer, occurred when the moisture retention, by weight of fabrics being dried, had decreased to about This will be recognized as a figure indicating substantial dryness of the clothes in the conventional sense, as opposed to bone-dryness.

Thus, the relative resistances of the two sensors 61 and 64 are used to provide the indication as to when the drying operation should be terminated. The cooling of sensor 61 virtually to atmospheric temperature causes the system to provide a reliable and accurate indication of the dryness condition of the fabrics.

Referring now to FIGURE 5, there is shown a modification of my invention wherein like numerals are used to refer to parts which are the same as those referred to above. In the structure of FIGURE 5, member 56 is secured to a relatively large member 110, formed of a material having good heat-conductive properties and arranged so that it has a substantial part of its surface exposed to the ambient air i.e., the atmosphere. The member 60 supporting humidity sensing grids 61 and 64 is then supported by this member 11%).

Member 110 functions as a heat sink, in effect, that is, the large amount of surface it has exposed to the ambient air causes it to be substantially at the temperature of the ambient air; this effect is enhanced when member 56 is formed of insulating material as shown. This means that member 60 is in an environment substantially at ambient temperature because of the heat sink thus provided.

It will be recognized that this, then, represents an alternative way of cooling the humidity sensing means to the temperature of the ambient air, that is, instead of a forced flow of ambient air over the surface of the sensing structure, a heat sink of the type shown may be provided. Also, of course, the two may be provided in combination to provide even more accurate and closer correlation between the temperatures sensed by grids 61 and 64.

It will be understood that while specific embodiments of my invention have been disclosed, other means of carrying out various aspects of the functions provided by my invention will readily occur to those skilled in the art. Thus, for instance, while a single member 60 supporting both grids 61 and 64 is preferred because structures made in this way provide closer correlation between the tracking characteristics of the two grids, it is obviously within the scope of my invention to have the grids separately mounted. By the same token, the output of the Wheatstone bridge may be monitored in different ways depending upon many factors such as the moisture level of operation, the allowable self-heat of the electrical components, the operating voltage level, etc. Thus, despite the illustration, for disclosure purposes, of one particular means of utilizing the bridge output it will readily be understood that many will occur to those skilled in the art and will be within the scope of my invention.

Therefore, while in accordance with the patent statutes I have described what at present are considered to be the preferred embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications (including, but not limited to, those listed directly above) may be made therein without departing from the invention, and it is therefore aimed in the appended claims to cover all such equivalent variations as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A fabric drying machine comprising:

(a) a fabric container having an air inlet opening and an air outlet opening both communicating with atmosphere;

(b) outlet conduit means for guiding air from said out let opening to atmosphere, said conduit means including a protected portion receiving a small air flow compared to the air flow through the remainder of said conduit means;

(0) means for circulating air into said container through said inlet opening and out of said container through said outlet opening;

(d) a heater positioned to supply heat to fabrics in said container;

(e) first humidity-sensing means in said protected portion positioned to be readily cooled substantially to atmospheric temperature;

(f) means for causing cooling of said first humiditysensing means substantially to atmospheric temperature;

(g) second humidity-sensing means positioned to sense atmospheric conditions;

(h) and control means responsive to a predetermined relationship of the humidities sensed by said first and second humidity-sensing means to effect termination of operation of said heater.

2. The apparatus defined in claim 1 wherein said means for causing cooling of said first humidity-sensing means to the temperature of atmospheric air comprises a heat sink member arranged adjacent said first humidity-sensing means and exposed to atmospheric air.

3. The apparatus defined in claim 1 wherein said humidity-sensing means are mounted on opposite sides of a single sheet of electrically insulating material, said sheet forming part of said surface of said protected portion.

4. The apparatus defined in claim 1 wherein said control means comprises a Wheatstone bridge circuit including said first and second humidity-sensing means as two legs of said bridge, said bridge being balanced when said humidity-sensing means both sense the same humidity, and means responsive to balancing of said bridge to effect termination of operation of said heater.

5. The apparatus defined in claim 1 wherein said control means includes a sequence control mechanism arranged to operate for a predetermined period at the beginning of a drying operation and then to terminate operation until said first and second humidity-sensing means sense substantially equal humidities, said sequence control means thereby being re-energized and eflfecting termination of operation of said heater.

6. A fabric drying machine comprising:

(a) a fabric container having an air inlet opening and an air outlet opening both communicating with atmosphere;

(b) outlet conduit means for guiding air from said outlet opening to atmosphere, said conduit means including a protected portion receiving a small air flow compared to the air flow through the remainder of said conduit means;

(c) means for circulating air into said container through said inlet opening and out of said container through said outlet opening;

((1) a heater positioned to supply heat to fabrics in said container;

(e) first humidity-sensing means in said protected portion positioned to be readily cooled substantially to atmospheric temperature by atmospheric air circulated over the surface of said protected portion;

(f) means for circulating atmospheric air over the surface of said protected portion;

(g) second humidity-sensing means positioned to sense atmospheric conditions;

(h) and control means responsive to a predetermined relationship of the humidities sensed by said first and second humidity-sensing means to effect termination of operation of said heater.

7. The apparatus defined in claim 6 wherein said means for circulating atmospheric air over the surface of said protected portion comprises structure for guiding the air drawn in by said air circulating means over the surface of said protected portion before the atmospheric air so drawn in reaches said heater.

8. A fabric drying machine comprising:

(a) a fabric container having an air inlet opening and an air outlet opening both communicating with atmosphere;

(b) outlet conduit means for guiding air from said outlet opening to atmosphere, said conduit means including a protected portion receiving a small air flow compared to the air flow through the remainder of said conduit means;

(c) means for circulating air included in said outlet conduit means, said air circulating means drawing air into said container through said inlet opening and out of said container through said outlet opening;

(d) a heater positioned to heat the air passing into said container;

(c) said protected portion having a part of its surface formed with first humidity-sensing means on the inside thereof and second humidity-sensing means on the outside thereof;

(f) means for guiding the air drawn in by said air circulating means over said surface of said protected portion before said air is heated by said heater;

(g) and control means responsive to a predetermined relationship of the humidities sensed by said first and second humidity-sensing means to effect termination of operation of said heater.

9. A fabric drying machine comprising:

(a) a fabric container having an air inlet opening and an air outlet opening both communicating with atmosphere;

(b) outlet conduit means for guiding air from said outlet opening to atmosphere, said conduit means including a protected portion receiving a small air flow compared to the air flow through the remainder of said conduit means;

(c) means for circulating air into said container through said inlet opening and out of said container through said outlet opening;

(d) a heater positioned to supply heat to fabrics in said container;

(e) first humidity-sensing means in said protected portion positioned to be readily cooled to substantially atmospheric temperature by atmospheric air circulated over the surface of said protected portion;

(f) means for cooling said first humidity-sensing means substantially to the temperature of atmospheric air;

(g) second humidity-sensing means positioned to sense atmospheric conditions;

(h) and control means operative in response to substantially equal humidities sensed by said first and second humidity-sensing means, said control means including a timer motor, first switch means controlling operation of said timer motor and said heater, second switch means also in controlling relationship to said timer motor, said timer motor causing closure of said first and second switch means during a predetermined initial period of an operation and then opening said second switch means, a control switch in parallel with said second switch means biased to closed position and movable to open position as long as said first and second humidity-sensing means sense different humidities, whereby said timer motor is de-energized by opening of both said second switch means and said control switch during the drying of clothes, and is re-energized by the closing of said control switch when the same humidity is sensed by said first and second humidity-sensing means to permit said timer motor to run and cause said first switch means to terminate the operation of said heater and of said timer motor.

References Cited by the Examiner UNITED STATES PATENTS 2,344,530 3/1944 Askew 23644 2,417,998 3/1947 Wales 34-48 2,643,464 6/1953 Halady 3448 2,820,304 1/1958 *I-Iorecky 34-45 3,170,774 2/1965 Deaton 34-48 X FREDERICK L. MATTESON, JR., Primary Examiner.

JOHN J. CAMBY, Examiner.

D. A. TAMBURRO, Assistant Examiner. 

1. A FABRIC DRYING MACHINE COMPRISING: (A) A FABRIC CONTAINER HAVING AN AIR INLET OPENING AND AN AIR OUTLET OPENING BOTH COMMUNICATING WITH ATMOSPHERE; (B) OUTLET CONDUIT MEANS FOR GUIDING AIR FROM SAID OUTLET OPENING TO ATMOSPHERE, SAID CONDUIT MEANS INCLUDING A PROTECTED PORTION RECEIVING A SMALL AIR FLOW COMPARED TO THE AIR FLOW THROUGH THE REMAINDER OF SAID CONDUIT MEANS; (C) MEANS FOR CIRCULATING AIR INTO SAID CONTAINER THROUGH SAID INLET OPENING AND OUT OF SAID CONTAINER THROUGH SAID OUTLET OPENING; (D) A HEATER POSITIONED TO SUPPLY HEAT TO FABRICS IN SAID CONTAINER; (E) FIRST HUMIDITY-SENSING MEANS IN SAID PROTECTED PORTION POSITIONED TO BE READILY COOLED SUBSTANTIALLY TO ATMOSPHERIC TEMPERATURE; (F) MEANS FOR CAUSING COOLING OF SAID FIRST HUMIDITYSENSING MEANS SUBSTANTIALLY TO ATMOSPHERIC TEMPERATURE; (G) SECOND HUMIDITY-SENSING MEANS POSITIONED TO SENSE ATMOSPHERIC CONDITIONS; (H) AND CONTROL MEANS RESPONSIVE TO A PREDETERMINED RELATIONSHIP OF THE HUMIDITIES SENSED BY SAID FIRST AND SECOND HUMIDITY-SENSING MEANS TO EFFECT TERMINATION OF OPERATION OF SAID HEATER. 